20 or so years ago a friend of mine and I booked on an eclipse charter flight to Luxembourg, it was scheduled to land just before totality, give us 2 hours on the ground to enjoy the eclipse, then take us back to London. The UK was only getting a partial. As we neared the airport, they announced over the speakers that there were two layers of cloud over Luxembourg, and we'd not see anything, but they had an offer for us, they'd got a new flight plan, they'd refuel, take off again and they had permission to do a couple of turns over Frankfurt where there was totality. So we watched it out of a little aeroplane window, got back to London for lunch. It was quite spectacular.

Where I am I will experience 95% of the eclipse, I could drive a few short hours but traffic is going to be so miserable. My family has a friend that has his own little plane. Maybe I can convince him to take me up and go watch it in the sky.

We'd be flying with only 4 passengers in a Citation CJ to allow window views for all. And these jets have windows twice the size of airliners (and a helluva lot cleaner/transparent). Our pilot is currently working on the flight plan, but he told me he already knew the airspace was gonna be crowded. More so than shown in Randall's cartoon. The good thing is that the FAA allows aircraft to be spaced at 1000 foot altitude intervals, and the CJ is good for 45,000 feet, so that leaves a lot of openings. Should be hearing from the pilot shortly on available flight plans. Won't be cheap, but the cool thing about seeing an eclipse from the air, say 30,000 feet, is that we'll be able to see the Moon's umbral shadow approaching and receding for close to 5 minutes both sides of the actual eclipse.

Eoink wrote:20 or so years ago a friend of mine and I booked on an eclipse charter flight to Luxembourg, it was scheduled to land just before totality, give us 2 hours on the ground to enjoy the eclipse, then take us back to London.

Humans...

Nonetheless, I will make sure I'm in South America come 2020-12-14. If not for the eclipse itself, then for traveling across Chile/Argentina.

Well if Trump decides to take a spin on AF1 to see this eclipse (which I seriously doubt) it'll screw things up for the rest of us. When AF1 is in the area it shuts down airport traffic and increases both horizontal and vertical required clearances. That sucker gets a LOT of open airspace, and it trumps (NPI) everything other than in-flight medical emergencies ... and it could override even that for "national security reasons" if it had to. Never done that to my knowledge. But that Bill Clinton haircut at LAX really messed things up for a lot of travelers.

Er ... uh ... There is no abrupt edge of a shadow as depicted. The eclipse begins an hour before, with the blockage of the Sun increasing towards totality, then decreasing for an hour after. In a vastly broader swath to the north or south of the path of totality, where the Moon "misses" the Sun a bit, it will also get much darker.

The reason to be in the path of totality, rather than just to the north or the south, is that you get to observe "Bailey's Beads", the Sun shining through valleys and mountain passes on the Moon, and the solar corona. I am told this is awesome; the emotional effect is deep and lasting, a lifetime of rational expectations turned upside down.

Unless there is an aircraft ceiling between you and the Sun, which will be close to zenith over the western US and the Pacific. Alaska Airlines is scheduling a "special eclipse flight" over the Pacific in the path of totality, to fly above any possible clouds, but only the pilots have windows that look upwards. If they roll the plane so that half the passengers can see upwards out their tiny windows, that would be exciting but distracting, and disappointing to the passengers on the north side of the plane.

BTW, an hour of reduced-to-zero sunlight is plenty of time for the upper atmosphere to cool down and drop below the dew point, and clouds to form, as happened to me when I attempted to watch the February 1979 eclipse in Central Oregon. Portland was completely overcast, but there were gaps in the clouds above the Goldendale Observatory in Washington, where I could have gone instead.

This year, I will watch from a friend's house in Idaho Falls. The chances of cloud cover there are less than 20% in August. Maybe. If his house is clouded over, and there are gaps in the clouds to the east, we can take a farm road to an alternative site. Except there will be 200,000 other visitors in the area with the same idea. Western Oregon, near home, will have higher chances of cloud cover, and vast hoards from California and Washington clogging I5 for days.

Which means the gasoline and food trucks can't deliver, the gas stations will run dry, the cars will stop, the drivers will spill into the countryside looking for gasoline and food, and chaos and violence will reign. Maybe this WILL be the end times. We'll get censored news of that in Idaho, where we will become serfs to the potato barons, pulling plows for a few spuds a day.

Added note: An excellent book about eclipses: Sun, Moon, Earth by Tyler Nordgren (who spent the 1979 eclipse in his bedroom in his Portland parent's house, watching it on TV). Presuming we will be stuck in Idaho during the Tribulation, I would appreciate suggestions for good books about Mormon eschatology.

Can it be a coincidence that Randall posted this comic exactly on the fourth anniversary of The End he himself inflicted upon us?

And yes, clouds forming because of the cooling of the atmosphere - that was exactly what prevented me too from observing the corona during the 1999 total eclipse in south west Germany. However, I at least had an elevated vantage point looking west over the Upper Rhine Plain, and the edge of the umbra advancing over the landscape (both the leading and the trailing one) was spectacular in its own way. Yes, the penumbra darkens the closer to the umbra you get, and still I remember observing a surprisingly noticable distinction between penumbra and umbra on the ground.

Eoink, you must be misremembering something though - Frankfurt was north of the zone of totality by some 80 kilometres (50 miles).

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keithl wrote:Er ... uh ... Maybe this WILL be the end times. We'll get censored news of that in Idaho, where we will become serfs to the potato barons, pulling plows for a few spuds a day. Presuming we will be stuck in Idaho during the Tribulation, I would appreciate suggestions for good books about Mormon eschatology.

I think you are confusing Idaho with Utah, but then I guess no place is a good place during the Tribulation.

keithl wrote:Added note: An excellent book about eclipses: Sun, Moon, Earth by Tyler Nordgren (who spent the 1979 eclipse in his bedroom in his Portland parent's house, watching it on TV). Presuming we will be stuck in Idaho during the Tribulation, I would appreciate suggestions for good books about Mormon eschatology.

keithl wrote: Maybe this WILL be the end times. ... Presuming we will be stuck in Idaho during the Tribulation, I would appreciate suggestions for good books about Mormon eschatology.

I think you are confusing Idaho with Utah, but then I guess no place is a good place during the Tribulation.

Google says:

52.51% of the people in Idaho, Idaho are religious, meaning they affiliate with a religion. 8.11% are Catholic; 26.78% are LDS; 9.55% are another Christian faith; 0.04% in Idaho, Idaho are Jewish; 0.25% are an eastern faith; 0.11% affilitates with Islam.

heuristically_alone wrote:Where I am I will experience 95% of the eclipse, I could drive a few short hours but traffic is going to be so miserable. My family has a friend that has his own little plane. Maybe I can convince him to take me up and go watch it in the sky.

I mean, you should do that anyway, because getting to ride in a private plane with a pilot they can potentially convince to do a barrel roll (other stunts are available) while they're up there is an experience everyone deserves to have at least once, if the option is open.

cephalopod9 wrote:Only on Xkcd can you start a topic involving Hitler and people spend the better part of half a dozen pages arguing about the quality of Operating Systems.

Steve the Pocket wrote:I mean, you should do that anyway, because getting to ride in a private plane with a pilot they can potentially convince to do a barrel roll (other stunts are available) while they're up there is an experience everyone deserves to have at least once, if the option is open.

keithl wrote:clouds to form, as happened to me when I attempted to watch the February 1979 eclipse in Central Oregon.

Whether (weather!) or not this was the reason, or just because it was the UK, I'll never forget the day I didn't see the Sun obscured in Cornwall, 1999.

At that time, I was enjoying pretty clear skies in Croydon (South London for those less familiar with British geography) and a high 90s percent coverage - giving the weird lighting, strange shadows, chill, etc of the deep penumbra, but not the full totality.

A few years later, I was in Ceduna (South coast of Australia for those less familiar with Australian geography) watching the eclipse there under moderately cloudy skies - a cloud cleared the sun a few minutes before totality, and the next one moved in a few minutes after totality ended.

keithl wrote:There is no abrupt edge of a shadow as depicted. The eclipse begins an hour before, with the blockage of the Sun increasing towards totality, then decreasing for an hour after. In a vastly broader swath to the north or south of the path of totality, where the Moon "misses" the Sun a bit, it will also get much darker.

Experiments with a large light source and small objects show that as the object recedes from the projection surface towards the light source, it starts with a sharp-edged shadow and almost no penumbra. Initially, the penumbra grows and the umbra brightens, then the border between umbra and penumbra fuzzes out, and the whole thing blurs into imperceptibility, with the whole process reversing as the object returns toward the projection surface. Maybe technically the edge of the umbra isn't actually sharp, but there's a fairly narrow transition region before the much broader penumbra.

And anyone who's been in a room with thick, well-fitted curtains on a sunny day will know that there's a sharp difference in room-illumination between almost completely closed and completely closed curtains.

keithl wrote:There is no abrupt edge of a shadow as depicted. The eclipse begins an hour before, with the blockage of the Sun increasing towards totality, then decreasing for an hour after. In a vastly broader swath to the north or south of the path of totality, where the Moon "misses" the Sun a bit, it will also get much darker.

And anyone who's been in a room with thick, well-fitted curtains on a sunny day will know that there's a sharp difference in room-illumination between almost completely closed and completely closed curtains.

You are correct, my error. Superficially, the cartoon edge looked like an abrupt transition from dark to daylight, about a mountain's width. But when I viewed the last cartoon panel on a 64 bit grayscale monitor, and properly adjusted the contrast settings (the slider that looks like aircraft windows, use cntl-alt-shift-U+1F60F while moving the mouse with your LEFT foot), I could view the panel with the correct luminosity gradations from umbra to penumbra.

Regards the religion of SE Idaho; you can't throw a stone in any direction without hitting an LDS Temple (unless you are within the Idaho National Lab fences, in which case you will hit an experimental breeder reactor, or an armed security guard). They are closer to Salt Lake City than they are to Boise. Fine with me; we have a big LDS church across the street, and they are good neighbors. When I was helping my next-door neighbor chainsaw a windfall tree, a couple of earnest young missionaries got off their bicycles and came over to help. Eye protection, black pants, white shirts, ties (tucked inside shirts for safety), adeptly wielding chainsaws - an image that will haunt me for life .

I think I have about a 50:50 chance of seeing a cloudless totality. After all, we're talking about the north Atlantic (near the Bahamas), during hurricane season. The ship will try to steer clear of clouds along the line.

One thing I would like to know: how much does altitude affect eclipse length time? (Because obviously as you approach the moon, the eclipse time approaches two weeks or so.) Would being on a high-altitude airplane increase totality by a few hundredths of a second?

I mean, sure, I'm probably being overly pedantic, but if this isn't the spot for that, I really don't know what is...

mathmannix wrote:One thing I would like to know: how much does altitude affect eclipse length time?

Well, it's actually a bit trickier than it looks. First off, the plane is moving, and that's your biggest effect. If you move at the speed of the shadow, you can make it last for hours.

But what if you are standing still? Well... what does that mean? The earth's surface is moving because the earth rotates. I presume you want to remain steady WRT the earth's surface. Well, in that case, the higher up you go, the higher your (earth's rotation) velocity will be. In the limiting case (umbra focuses to a point on the surface, leaving just an instant of totality on the surface), being as high up as the moon (and rotating at the speed of Earth's rotation) will lead to totality lasting as long as it takes for the earth to move half a degree of arc (which is how much the moon subtends in the sky). That's 1/720 of a day, or 12 seconds The added time is proportional to the ratio of your altitude to the moon's altitude. At one (5000 foot) mile up towards the (240,000 mile away moon), you could extend totality by 12/240,000 seconds, or one twenty-thousandth of a second.

In the real case, the umbra doesn't focus to a point on the earth's surface, but can be idealized to focus on a point below the earth's surface. How far below depends on the exact orbital position (distance) involved at the moment of eclipse.

Typical totality on the earth's surface lasts several minutes. Earth rotates 365 degrees per day. The moon goes around once a month; its contribution to length of totality is minimal and can be neglected for now (add it in later). The rest is an exercise in geometry, left for the reader.

Jose(edit: moon subtends half a degree, not one degree)

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mathmannix wrote:One thing I would like to know: how much does altitude affect eclipse length time? (Because obviously as you approach the moon, the eclipse time approaches two weeks or so.) Would being on a high-altitude airplane increase totality by a few hundredths of a second?

I mean, sure, I'm probably being overly pedantic, but if this isn't the spot for that, I really don't know what is...

The answer provided by ucim was good and covered much of what you asked. I'll add to that. I'm planning just such an adventure and looking at chartering a jet or a turboprop (each with its pros & cons). The flight plan I submitted to the charter companies was a compromise between "chasing the shadow" to lengthen the eclipse, and orienting the aircraft during totality for a perpendicular view through the windows (reducing reflections for photography). We could gain almost 30 seconds on the jet (450 mph) and about 20 seconds on the turboprop (300 mph).